The United States' market-government hybrid mortgage system is unique in the world. No other nation has such heavy government intervention in housing finance. This hybrid system nurtured the excessively risky loans, financed with too much leverage, that fueled the U.S. housing bubble of the last decade and resulted in the systemic collapse of the global financial system. The responsibility for the massive failures of the government-sponsored enterprises (GSEs) Fannie Mae and Freddie Mac, at the center of American housing finance and the private securitization system that supports housing finance, falls directly on regulators and indirectly on their political overseers.